Drawn from the letters 'S' and 'D,' the San Diego Soda is created by the addition of feces (Shit) and semen (from the Dick) to a soda. The addition can be direct, or indirect by a boy or girl placing anything that has come in contact with those substances on or near said soda.

Gary: "Yo Matt, did you just take a sip from Tom's soda? You know he licked some guy's asshole and then sucked his dick last night."
Othello: "Oh damn son, you just drank a San Diego Soda."